1. Field of the Invention
The invention relates to a process for reducing the aluminum content of neopentasilane by treatment with organic compounds.
2. Description of the Related Art
Neopentasilane (NPS, tetrakis(trihydridosilyl)silane) can be used as a precursor for the deposition of silicon-containing films by means of chemical vapor deposition (CVD). The advantage of NPS lies in the high deposition rate of Si or SiC in the CVD operation, and the comparatively low deposition temperatures compared to other silanes (J. C. Sturm, K. H. Chung, ECS Transactions 2008, 16, 799-805).
Suitable synthesis processes for preparation of NPS on the industrial scale are described in WO 2008051328, WO 2010043551 and WO 2010149547.
WO 2008051328 describes the reaction of hexachlorodisilane (HCDS) with tertiary amines as catalysts to give dodecachloroneopentasilane (CNPS). This route to neopentasilanes was improved in WO 2010043551 using ether compounds, more particularly tetrahydrofuran (THF), as catalysts. In the second step of the preparation process described in WO 2008051328, the resulting dodecachloroneopentasilane is reduced with diisobutylaluminum hydride (DIBAH) to NPS. The process, however, has the disadvantage that the resulting NPS, in spite of purification by means of distillation or condensation, still contains distinct proportions of organoaluminum impurities (in particular diisobutylaluminum chloride (DIBAC)). However, aluminum as a dopant element influences the semiconductor properties of silicon, and so the content of aluminum has to be reduced to a minimum for many applications of silicon-containing films.